From BlenderWiki

Introduction

The user interface enables interaction between the user and the program. The user communicates with the program via the keyboard and mouse, while the program response is on the screen.

If you are new to Blender, you should learn its user interface before you start modeling. The concepts behind Blender’s interface are specifically designed for a graphics modeling application and the vast array of features are different from and organized differently than other 3D software packages. In particular, Windows users may need to get accustomed to the alternate manner that Blender uses to handle such things as button choices and mouse movements.

Blender’s Interface Concept

This difference is one of Blender’s great strengths. Once you understand the Blender methodology, you will find that you can work exceedingly quickly and productively. Some features are familiar, like the top menu bar of File, Add … Help. However, many other features are quite unheard of in most (if not all) other applications. For example:

Blender windows cannot overlap and hide each other, one exception being a small number of mini-floating panels which are transparent, foldable, small, and dockable.

Blender relies heavily on keyboard shortcuts to speed up the work.

Blender’s interface is drawn entirely in OpenGL and every window can be panned, zoomed in/out, and its content moved around.

Your screen can be organized exactly to your taste for each specialized task and this organization can be named and memorized.

These key differences (and many others) make Blender a unique, powerful, and very nimble application, once you take the time to understand it.

The interface can be broken down into several key areas: windows, contexts, panels, and buttons (controls). For example, the buttonswindow contains context buttons which show different groups of panels and the panels each show groups of buttons. These principal areas are discussed on the following pages.